Sec 5 Soil, Plant, Water Relations

Soil, Plant, Water Relations Plants and Water Water makes up about 50% of the tissue in a woody plant and about 80-90% of the tissue in an herbaceous plant. Water plays a key role in the following plant functions: 1. Photosynthesis In photosynthesis carbon dioxide and water are converted to sugars and oxygen. When stomata are open C02 and O2 are exchanged and evaporation of water takes place (transpiration) 6CO2 + 6H2O ------> C6H12O6 + 6O2Sunlight energy 2. Transpiration of water Transportation of nutrients Plants pick up nutrients from the soil in soluble form. These nutrients are then transported up through the plant through transpirational pull (cohesion and tension). The evaporation of water from the leaves creates a negative pressure gradient that draws more water up from the roots. As long as there is water in the soil equal to the rate of evaporation the process will continue. If soil water depletes or evaporation exceeds available water the plant will go under stress. About 1% of the water that the plant takes in is used for photosynthesis. The rest is used for transpiration. One of the major causes of desertification is the removal or destruction of plant material especially in arid and semi-arid regions. This includes deforestation and agriculture practices like overgrazing. 3. Control of plant temperature Transpiration also acts like a type of evaporative cooling. It will help keep the plant cool in hot weather. The amount of water needed by plant material varies substantially. Weather factors that contribute to water use are sun, wind, air temperature, humidity and rainfall (taken from Irrigation Association) Sunlight – solar radiation is the most important weather related factor in transpiration and evaporation Sunlight is measured by intensity and duration. It is influenced by microclimates, time of year, cloud cover, altitude, topography, buildings etc. Wind is measured in terms of velocity, direction and duration. It increases transpiration and evaporation rates as it moves across the surface of the leaf or soil. Wind can be influenced (either more or less) by other vegetation, and hard landscape features like buildings and fences. Air temperature – the higher the air temperature the faster the evaporation and transpiration rates. Humidity – according to National Geographic.org humidity is the amount of water vapor in the air. If humidity is high, transpiration rates slow down. If humidity is low, transpiration rates will increase. Rainfall – depending on where you are in the country, rainfall can supplement irrigation or irrigation can supplement rainfall but not all the rain is available to the plant. Depending on the soil texture, structure and topography a heavy rain (high intensity for a short period of time) can create runoff or go too far down into the soil profile to be available to the plants. Fine mists of rain will often sit on top of mulch or thatch and not percolate into the soil profile. A plant with a large canopy can deflect rain off ground cover plants beneath it. Plant Adaptations A plant’s need for water will vary depending on species, maturity, health and exposure. Some plants are adapted to storing water or decreasing transpiration by developing leaves that are reduced to spines, contain wax or hair coverings, fold up or are able to store water. The initiation of deep roots when a plant is first developing will also help combat drought conditions later on. Drought Stress Drought can show up in plant material in many different ways because water is responsible for many plant functions including photosynthesis, nutrient uptake/transport and cell turgidity Some of the more common signs of drought stress include: Slow growing or stunted plants ( long term drought) Wilting of the leaves, loss of sheen Yellowing of the leaves Leaves turn crispy Leaves drop (thinning of the canopy) Leaf necrosis (burning on the leaf margins) But be aware - These symptoms can be similar to overwatering or nutrient issues. Evapotranspiration Is the combined effect of evaporation off the earth’s surface and transpiration from the plant. Evapotranspiration rates are calculated using weather data and a reference plant species. The reference plant species used in Landscapes is cool season turf grass grown to 4-6” in an ideal situation. This is classified as reference ET (ETo) ETo is expressed in inches or mm per unit of time eg: mm/day, inches/month. Evapotranspiration rates can be calculated or data can be taken from a number of resources. Alberta Agriculture, and Alberta Environment both calculate ET rates Alberta Agriculture - Alberta Climate Information Service Website: https://agriculture.alberta.ca/acis/ Adjusted ET Landscape coefficient (KL) A more accurate ET rate for landscape plants can be established by multiplying the reference ET by a Landscape Coefficient. The Landscape Coefficient takes into consideration, type of plant, vegetation density and microclimate. It is determined using one of the following formulas KL = KT x Kmc KL = KP x Kd x Kmc KL = Landscape Coefficient KT = turf coefficient The following chart, taken from the Irrigation Association, lists the coefficients for turf applications Grass Type High performance (Lush ) Acceptable appearance Low maintenance Cool Season 0.80 – 0.85 0.70 – 0.75 0.60 – 0.65 Warm Season 0.70 - 0.75 0.60 – 0.65 0.50 – 0.55 High performance would be a turf area that takes extra care such as sports fields or golf greens. Acceptable can also be called traditional. If the lawn is in a residential lot or well maintained park it would be classified as acceptable. Most turf areas will fall in this category. Low maintenance refers to turf in industrial areas or along roadways. KP = Plant coefficient The following chart taken from the Irrigation Association outlines the plant coefficients. Plant Type Max appearance (lush) Acceptable appearance Low maintenance (lean and green) Trees 0.9 - 0.95 0.70 – 0.75 0.45-0.50 Shrubs 0.60 - 0.65 0.45 – 0.50 0.30 – 0.35 Desert Plants 0.40 – 0.45 0.30 – 0.35 0.20 – 0.25 Ground cover 0.70 – 0.80 0.50 – 0.60 0.30 – 0.40 Mixed Lscp 0.90 – 1.00 0.75 – 0.80 0.50 – 0.55 Professional Horticulturists know that all trees do not take the same water and shrubs vary substantially in their water requirements. The irrigation scheduler will have to evaluate each situation and determine whether the type and age of plant material he/she is dealing with needs a little more or less water. Kd = vegetation density Vegetation density refers to the amount of leaf material that covers the ground. Density is affected by the type of plant material, the plant spacing and the maturity of the plant material. As density increases transpiration increases as does the plants' need for water. The factors for plant density are as follows: Plant type ¼ to ½ ground shaded ½ to 2/3 ground shaded Over ¾ ground shaded Low growing plants <45cm tall 0.35 - 0.45 0.60 – 0.75 0.80 – 0.95 Small shrubs 1 – 1.5m tall 0.35 – 0.50 0.70 – 0.80 0.85 – 0.95 Large shrubs, trees > 4m 0.40 – 0.55 0.75 – 0.95 0.95 – 1.00 Turfgrass n/a n/a 1.00 Irrigation Association – Landscape Irrigation Auditor 3rd Edition February 2013 pg 109 (plant sizes converted from imperial to metric measurements) Kmc = microclimate In most urban landscapes there are many microclimates that affect water use. Plants growing in the sun will use more water than plants growing in the shade. Plants facing south up against a building or concrete walk will use more water than those planted in a mulched bed in the middle of a lawn. The irrigation scheduler must determine the effect the climate has on the water use of the plant. The following microclimate factors were taken from the irrigation auditors handbook through the Irrigation Association. Vegetation High Average Low Turf/Lndscp Plants 1.2 – 1.4 1.0 0.5 – 0.8 Examples of high microclimate would be the south side of buildings, reflected sunlight or concrete Examples of low would be shady areas or more moist areas. Average is neither harsh nor helpful Example: A bed of mature small mixed shrubs is located in a residential landscape up against a brick wall facing west. The plants are planted close together so the overall coverage is more than ¾ of the soil KL = KP x Kd x Kmc KL = 0.5 x 0.85 x 1.2 = 0.51 The Landscape coefficient is 0.51 If the reference ET rate for this area was 5.7mm/day, the reference ET rate would be 40.39mm/wk or 178.87mm/month (7.04”/month) (this is worst case scenario – ET rates refer to the average for the month of July or August) The landscape ET or adjusted ET rate would be ETL = ETo x KL 40.39mm/wk x 0.51 = 20.60 mm/wk or 91.22 mm/month (20.60 x 4) For scheduling purposes we can assume this is how much water is going to be used in the time indicated. Water in the Soil The following terms are used to describe water in the soil: Infiltration rate – the rate at which water enters the soil profile. Usually described in inches/hour or mm/hour Infiltration rates will vary depending on soil texture, structure, compaction, and % moisture already in the soil. Percolation – the process of water moving through the soil profile. Water percolation rates and patterns will vary depending on soil texture and structure. Percolation through a fine soil will travel horizontally and vertically whereas water movement in a coarse soil will be more vertical. https://www.soils.org/discover-soils/soils-in-the-city/green-infrastructure/how-nature-manages-water Water Movement is also affected by structure and gravitational pull. Water will move through the soil through the large pore spaces. Water Storage Saturation – saturation occurs when all the pores in the soil profile are filled with water. Field capacity – field capacity occurs when the larger pores in the profile have drained due to gravitational pull and only the water or capillary pores are filled with water. Field capacity is measured approximately 24 -48 hours after the soil has been saturated to allow natural drainage to occur. PWP – permanent wilting point is when there is only water around the soil particles. This water creates a tight bond around the particles and is not available to the plant material. At permanent wilting point plants will show signs of stress. Available water – available water is between field capacity and permanent wilting point. Available water varies depending on soil texture. The following chart shows the amount of available water in a soil profile by texture. https://www.noble.org/news/publications/ag-news-and-views/2001/september/soil-and-water-relationships/ Available water is measured in inches/foot, inches per inch or mm/cm Plant available water – Plant available water is the amount of water that is available to the plant. It is the available water x the root zone PAW = AW x RZ Allowable depletion – this is the % of water that can be depleted from the soil profile before irrigating. Allowable depletion depends on the plant material being irrigated. Management allowable depletion is defaulted to 50%. Allowable depletion allows the irrigation manager to determine how often to irrigate. "Soil Moisture and Irrigation ." sensor.com, soilsensor.com, soilsensor.com/soil/soil-moisture-and-irrigation/. BASIC SCHEDULING ( Appendix C page 47 Best Management Practices, Irrigation Association) Determine: when to irrigate, how much to irrigate, how long to irrigate How much water to replenish the root zone AW x RZ x MAD AW = available water ( in/mm/ft) x root zone (in/mm/ft) x management allowable depletion ( decimal) Example a silt loam soil under turf with a root zone of 8” MAD 0f 50%Silt loam AW = 2”/foot ( from chart)Turf root zone = 8” = .666ft 2 x .666 x .5 (MAD) = .67” water .67” = 17mm FYI - 1L of water will water 1m2 of land 1mm deep. therefore you will need 17L of water per m2 of land. For 100m2 of land you will need 1700L of water. When to irrigate is based on the allowable depletion. If the available water in a silt loam is 2.0” per foot of depth, the root zone depth is 1 foot and the Management Allowable depletion is 50%, then irrigation needs to be applied when 1” of water has been depleted. If the ET rate of the plants is .25” per day then water would have to be applied every 4 days. Try these How often would you water a sandy loam soil with shrubs that have a root zone depth of 1.5 ft If the average ETL rate is 0.1” per day and the MAD is 50%. How often would you water a fine sand planted with annuals that have a root zone of 1ft. MAD = 50%, ETL = 0.3” per day How often would you water a vegetable garden with a fine sandy loam if the root zone was 6”, the MAD is 40% and the ETL = .2” per day? How much water to apply can be determined by using the ET data per day. If the ET on day 1 was .15 inches, on day 2 was .20 inches and on day 3 was .15 inches then on day 3 when irrigation is applied a total of .5 inches needs to be applied to “top up” the soil water. To determine irrigation run times (how long to irrigate) Step 1. Determine the plant water requirement[ETL]. ETL = ETo × KL eg: .62 × .70 = .43 inches Step 2. Determine irrigation run time [RT]. RT = ETL × 60.43 x 60 = 19 minutes PR 1.34 in./h Try these: The landscape ET for a system is .39 inches and the precipitation rate is 1.25 in/hour. How long would you set the controller to run? If the ETL of a system is .56 inches and the precipitation rate of the sprinklers is 1.39”/hour How long would you set the controller. The reference ET is .53 and the landscape coefficient is .80. If the precipitation rate is 1.30”/hour how long would you set the controller to run? If the reference ET is .44 and the landscape coefficient is .65 What is the ETL? If the precipitation rate was 1.10” per hour how long would you set the controller? If the reference ET is .48 and the landscape coefficient is .75. how long would you set a controller to run with sprinklers that have a precipitation rate of 1.26”/ hour. A basic way to calculate Landscape Water Requirements is through the following formula LWR = (ETo x KL) -R x LA x 0.623 IE LWR = Landscape Water RequirementsETo = Reference ETKL = Plant coefficient R = rain expected LA =Landscape area0.623 = constant to convert inches to gallons of water IE - irrigation efficiency AnswersWhen 1. AW = 1.25”/ft; RZ= 1.5 ft; ET = .1”/day; MAD = 50%1.25 x 1.5 x .5 = ,938” divided by .1 = 9.38 days or 9 days2. AW =.75”/ft ; RZ = 1 ft; ET = .3”/day; MAD = 50%.75 x 1 x .5 = .375” divided by .3 = 1.25 days or every day3. AW = 1.5”/ft RZ = 6” or .5 ft; ET = .2”/day; MAD = 40% 1.5 x .5 x .40 = .3” divided by .2 = 1.5 or 1 dayIrrigation Run TimeRT = ETL x 60 PR 1. .39 x 60 = 18.14 minutes 1.29 2. .5 x 60 = 21.58 minutes 1.39 3. .53 x .8 = .424” ETL .424 x 60 = 19.57 minutes 1.30 4. .44 x .65 = .286” ETL .286 x 60 = 15.60 minutes 1.10 5. .48 x .75 = .36” ETL .36 x 60 = 17.14 minutes 1.26 Resources http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/environmental/drought.aspx (drought stress list) www.thetreegeek.com/problems/drought-stress ( drought stress list) available water https://www.noble.org/news/publications/ag-news-and-views/2001/september/soil-and-water-relationships/ percolation pattern https://www.soils.org/discover-soils/soils-in-the-city/green-infrastructure/how-nature-manages-water Irrigation Association – Landscape Irrigation Auditor 3rd Edition Fairfax VA; February 2013 Editor – Robert D. von Bernuth Irrigation Association – Principles of Irrigation 3rd Edition Fairfax VA; March 2015 Editor – Robert D. von Bernuth Grass Type | High performance (Lush ) | Acceptable appearance | Low maintenance Cool Season | 0.80 – 0.85 | 0.70 – 0.75 | 0.60 – 0.65 Warm Season | 0.70 - 0.75 | 0.60 – 0.65 | 0.50 – 0.55 Plant Type | Max appearance (lush) | Acceptable appearance | Low maintenance (lean and green) Trees | 0.9 - 0.95 | 0.70 – 0.75 | 0.45-0.50 Shrubs | 0.60 - 0.65 | 0.45 – 0.50 | 0.30 – 0.35 Desert Plants | 0.40 – 0.45 | 0.30 – 0.35 | 0.20 – 0.25 Ground cover | 0.70 – 0.80 | 0.50 – 0.60 | 0.30 – 0.40 Mixed Lscp | 0.90 – 1.00 | 0.75 – 0.80 | 0.50 – 0.55 Plant type | ¼ to ½ ground shaded | ½ to 2/3 ground shaded | Over ¾ ground shaded Low growing plants <45cm tall | 0.35 - 0.45 | 0.60 – 0.75 | 0.80 – 0.95 Small shrubs 1 – 1.5m tall | 0.35 – 0.50 | 0.70 – 0.80 | 0.85 – 0.95 Large shrubs, trees > 4m | 0.40 – 0.55 | 0.75 – 0.95 | 0.95 – 1.00 Turfgrass | n/a | n/a | 1.00 Vegetation | High | Average | Low Turf/Lndscp Plants | 1.2 – 1.4 | 1.0 | 0.5 – 0.8